"Every country understands that hitting a military jet can start a war," politician Gennady Gudkov told Ekho Moskvy radio station, saying that is why every possible warning step is taken before shooting a plane down.

Many commentators here have cast doubt whether that happened in this case.

"There was no warning. Not via radio, or visually. There was no contact at all," the surviving co-pilot of the plane told journalists, safely back at Russia's airbase in Syria after his emergency mid-air ejection.

He says the jet was shot down from behind.

"If they had wanted to warn us, then they could have shown themselves - flown in parallel," Captain Murakhtin said.

Unconfirmed audio recordings have now been released by the Turkish military, said to be orders for the plane to change course. But the co-pilot insists he did not enter Turkish airspace "even for a second".

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Media captionIn the audio recording from the Turkish military, a voice can be heard repeatedly saying ''change your heading south immediately''

Russia's foreign minister has called the decision to shoot down the plane a "planned provocation", without speculating on Turkey's supposed motive.

But President Putin has already accused Ankara of siding with Islamic State (IS) by hitting the Russian jet; he also claimed some in Turkey are benefitting from the illicit sale of IS oil exports.

Clearly furious, he has threatened "serious consequences". After all, these are the first military casualties for Russia since air strikes began in Syria.

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Russian President Vladimir Putin has accused Turkey of being the "accomplices of terrorists"

But so far concrete measures have been limited.

Russia has broken off military contacts with Turkey but diplomatic channels remain open.

The foreign minister spent a fraught hour on the phone to his Turkish counterpart today, but his conclusion was critical: "We do not intend to go to war with Turkey," Sergei Lavrov assured the world.

Clear message

Instead, ministries have been ordered to report back to the Kremlin on any projects involving Turkey, for a decision on possible sanctions.

The future of a pipeline project could be in doubt and there have been calls for flights to Turkey to be suspended.

Meanwhile, tourists have been warned against travelling there for "security reasons". Last year, Turkey was the destination of choice for over three million Russian holidaymakers.

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The sophisticated S400 anti aircraft system is also being deployed to bolster air defences

On the ground inside Syria the changes have been more immediate.

A cruiser has been despatched to help bolster air defences around the Russian base.

The sophisticated S400 anti aircraft system is also being deployed and Russian planes will now be protected on bombing raids by fighter jets.

The message to Turkey and its allies is clear: don't dare try it again.

As for the rescued co-pilot, he says he is impatient to return to the skies.